of Africa, Asia, and Latin America as a whole, life expectancy in the deca of the 1920's was probably less than 35 years, lower than it was in 1840 western Europe, Canada, and the United States. An extremely rapid rise life expectancy and a corresponding decline in death rates occurred duri the first two decades after World War II, and is still continuing, thov, probably at a slower rate.
The reasons for this remarkable change are not entirely clear. One ca was certainly the widespread control and virtual elimination of malaria : some other insect-carried diseases. Others were the widespread use in r\ areas of the less developed countries of vaccines and modern drugs, impro drinking water and sanitation, and better personal hygiene. All these pu health measures, the products of modern technology, are relatively inex] sive and easy to use in the absence of much improvement in economic co tions. But improved nutrition resulting from greater abundance and be distribution of food supplies and some rise in per capita incomes have p ably also been important factors in many regions. Famines on a widesp scale have been absent or infrequent owing to improved transportation communications, and to greater concern for the welfare of the poor coun among food-surplus nations. There has been some speculation that hi beings have developed more immunity to some microbial diseases or tha virulence of some microorganisms has declined. The period from the 14 the 19th centuries has been called the "golden age of bacteria."
Recent Changes in Fertility in Some Less Developed Countries
In a few less developed countries there has been a significant dec! birth rates during the last 10 to 15 years. On the other hand, in at leasl countries where birth rates are still high, these rates have apparently somewhat during recent years, probably because of greater survival and health of mothers during their later reproductive years.
From 1960 to 1967 seven poor countries achieved declines in thei rates of 20 to 35 percent: Taiwan, Hong Kong, Singapore, Mai Barbados, Trinidad and Tobago, and Albania. Seven others showed d of 12 to 19 percent: West Malaysia, Ceylon, Reunion, Jamaica, Puert Chile, and Costa Rica. These rates of decline are much higher than t the present developed countries during their period of demographic tion. Several other countries in Latin America seem to be approaching of fertility decline: Guiana, Venezuela, Panama, and Mexico.
In most of these countries there has been a substantial measure nomic development and, particularly, social change, including not! provements in education, communication, social infrastructure, ; expectancy. Several of them have experienced a high per capita i from the rich countries. The evidence of the